Centrifugal valve for fluid clutches



Dec. 2l, 1954 v H, F, HQBBS 2,697,441

' CENTRIFUGAL VALVE FOR FLUID CLUTcHEs /n yen f' How/1R19 E H0525 57W@ www H. F. HOBBS CENTRIFUGAL VALVE FOR FLUID CLUTCHES Dec. 2l, y1954 Filed oct. 1o, 1952 2 2 s KfZ/W7 W77/ /w/ 7//4 Z7\ m n /f w Mui a 9 win mais?. s l

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United States Patent JEOilce CENTRLFUGAL VALVE .Fok lc-LU/Tc'rins Howard Frederick Hobbs, .Leamington 'Spa, `,EnglL"assignor lto Hobbs Transmission Limited, .Leamington Spa, Englandra British vcompany Application october1o,1=9sz,"se1ilNo. 314,102

the other endiso las to permit'movement of Isaidv -valve element under centrifugalaction, ythe'outer vend 'ofssaid valve borefbe'ing permanently lclosed againstjescape--of fluid therefrom, resilient meansfacting Von fthe valve Aelement, and suitable ductsorfporfts controlled Aby the'valve element. An example of :such ya valve'is described fin' the specification of Vour jBr'itish Patent lvNo. "63'73'25'1f'andmay be used in fconfjunction with anotherlvalve 4in ille-'housing fasv disclosedin the'fsa'id specification. y'Th'ebjectfoi the inventionis the 'provision of V'an improvedvalve,v which is actuated by centrifu'galfforce'toprovide vk"smooth automatic engagement of the c'lutc'h when `Ysome'fpr'ede't'ermined speedis reached; prevents elu'tc'hengagernent :at low speedswhich might stall the engineg-fand which`v/ill permit engagement'of the clutch vwhen the y'clutch -housing, which carries the valve,""isy stationary, sothatina vehicle the engine can ge s'tartedbytowing for-running downhill.

According to the invention, ahydraulicallyiactuated friction'clutc'h has a`rotary housing enclosing frictionelements, 'a pressure kspace vin' said housing for yreceiving Huid under pressure for engaging the'frietion''elements, a valve bore in said housing, a`i`1r`st inlet fduct and ia iifrst outlet duct `vin said housing Ifor supplying 'uid Iunder pressure to and -exhaustingsaid `'fluid `from-fsaidval-ve` bore respectively, said outlet duct being located adjaee'nt said valve fbore, a movable' valve element-in'sa'idbor'e, said valve bore being'disposed withone end further 'from the axis of the said Ahousing than lthe fotherend "so 'sto permit movement of said valve elementu'nder centrifugal action, the louter fend of said 1Val-ve Iborebeingjperrnaf nently closed against escape of iluidthere'frorm xsaid Avalve element having openings whereby safid linlet 'and outlet ducts are brought -into y'communication '-vvhen T'Said valve element is in 'an intermediate position in Asaid"valve ore; for exhausting fluid`underpressureresilient meansf-ac ng o'nsaid v'alvcelement iin -opposition to movement-'o 'said valve 'element' caused by centrifugal Eforce and servi-n: to keep said valve element vvin 'exhaust"closing positiens'dun4 ing conditions of 'said housing fromand inclndingfstationary, to a low predetermined"speed'ofro'tation there-v of, asecond inlet duct'in said,housing'leadingffromsid pressure space "to I'the outer end 4ofthe vsaid valve lbore, serving to'open ythe pressu`re`to-`the -ote'r end-'of said Valve element fwhereby the pressure yacts on t-heffelcnient in 'opposition to `-movement of'sai'd =valv`e yelern'en't--caused nby centrifugal force, and'a'secondfotlet duct controlledbyv said valve element toV open "tothe oute'rfeknd tlresaid valve bore just prior to 'commencing 'the inwiardiclosmfg A According -`to` a vvrnodifcationo'ft-he "invention" the `clutch has a second movable valve element inlth'einnerend :of said bore, said second jvalve 'element `being 'adapted to close said 'rst outlet duct Ianda second resilient means acting on the said vsecond valve 'element ifn i 's'am'e direction as centrifugal force 'tendingto irnovefsa'i'd se'cond valve felenent to the .outlet l'closing position,

" .Fi'gfshows the clutch engaged-:forover-run starting;l

v 2,697,441 Patented Dec'. 21, 1954 12 h l(l)- An exhaust 'which renables Athe l clutchtorbecome disengaged 'while :the-'engine risrunning 'at idling isp'eeds.

stantially 'but not .wholly free Iso V"that immediate .response 'is obtained 'when :speeds are increased, and so ythat on over-runthere will' be 2a .drag which increases with-engine speed and' whichflwill ensure that the clutchl'is automatically brought` into engagement.

1(3) .A vgradual build up .in engaging pressure in lac- `cordance`1 with 'speed and a tinal `exhaustclosingaction whereby the .fullf pressure suppliedato 'the vc'lutchais main-y tained -on the'friction surfaces.

all feihausts iare 'closedso as to'enableffor example, '1an engine to 'be started'fby .towing orI running 'a vehicle-down'.

hill.

(.5) Means ltdpreventcondition' (4),and consequent j'Ehe :invention will now be .further described by wav of example with 'reference-:to `the vaccompanying diagram.-

matic drawings wherein lFigures 1,12, 3 and 4 are sect1onal views :in a lplanev containing the 'axis ofla :clutch made I1n accordance Awith the invention showingonly parts yconcerned 'in thefprescnt -invention but showing the fvalve in different positions 'of operation.

'Fig. l showsthe clutch engaged;

.Fig. .2 vshows 'the -clutchparti'aliy 'engaged (during 'take up of. clutch);

and c,

,-.Fig. 4 'shows' the clutch disengaged.

This valve may .replace the valve 5 -in the apparatus shown in -specilication 'of our British .Patent k637,251.

Accordingto' one construction form of the'invention, a .rotary-housing, part'of`whicl1is shown 10, lil, en-

closes friction iele'rnents'. vThe pressure :plate 112"com` prises' one fof vthe friction elements, `to .engage another friction y.element `(not shownr) such 'as a spinnerplate The vfriction element '12 .is

flexible JAring shaped diaphragm 13,"between which tand the pressure-.plate lis ranfinsulating'ring .14. The'fpartI of the housingIL hereinafter lreferred :to as the valve body,

is so shaped as to provide an annular `space 15 behind thedaphragm. This :serves "as a Iliquid pressure 'space to'whichiliqu'id'v is suppliedfor engaging the clutch., while exhaust Y'ofliquidrorn said rspace enables the clutch to be'disenga'ged. `The valve body risjprovided with a radially disposed Icylindrical'bore lfwhich'contains aslidable valve-piston 17. The youterend of the lbore 'is closed by cap "18. .Aspring v19 isprovidedin the bore, "one end ofiwhich abuts against the cap and the other fend .of which engages 'against ythe 'slidable piston. An inletduct A20,

herein'zreferredto asthe second finlet duct ,leads/from Athe pressure'space in the yalvebcdy to the lcylindrical bore -sothat 'at alltni'espressure acting in the Jspace Calso acts on "the outer of 4.'theslida'ble piston, .iq-e. into space 2%, tending to move vit inwards. -The outer fendbf the alwaysuncovered The yirmer'ffend 'of- Ithepiston :has a central .drilling 21 `fvvhi'ch is'connejcted by'cros's drillings 22`t'oa'n fannularfgrooveja. The bore fis connected. to the-pressure .'spa'ce 35 lby another drilling M-referred toas theiirst vinlet duct-andincertain positions such fa's shown infFigure'4,1thegroove23 will Icommunicate with the first inlet duct 24 so Vas to allowpres'sure to escape through thefdrlflingin 4the piston. A .further .drilling ".25 is' prcvidednear 'the-sinner end of the bore, herein v:referred to as -the frs'tfoutlet-duct,v:for`exhaustinglthe liquid from A valveconstructed liniaceordne'ewilllfthe'invention provides; l

This exhaust-closed condition is maintained from the stationary condition of the housing up to a low predetermined speed i. e. a speed below the idling speed of the engine but sufficient for starting of the engine so that a small predetermined pressure is built up in the space 15. The speed of the housing will then rapidly increase to idling speeds and during this increase the piston 17 will move out, momentarily opening the duct 24 to space 34 and duct 30 to space 26 but immediately reaching the idling speed position of .Figure 2 in which the ducts 2-4, 30 are closed by the piston. When in the outermost position (during normal running at higher speeds than idling) shown in Figure 1, the first inlet duct 24 is also closed, so that in the positions of both Figures l and 3 there is no communication between first inlet duct and first outlet duct and fluid pressure can be built up within the pressure space 15. When in an intermdiate position,.

shown in Figure 4, the groove inthe piston will mate with the first inlet duct 24 and the pressure can therefore escape through drillings 21, and the first outlet duct 25. Also in this intermediate position, the second groove 29 is so located that further inward movement of the piston will open the groove to the .second outlet duct 30, and thereby the space 26 at the outer end of the piston to exhaust. The mass of the piston is so arranged that over certain selected speeds of au input member to which the rotary housing 10, 11 is attached, such as given with an engine when idling, the piston takes up the said intermediate position and is held in this position against the action of centrifugal force by the liquid pressure acting on the outer end of the piston, which4 is assisted by the spring 19. At higher speeds, the piston will tend to move outwards, thereby tending to close the first inlet duct and causing increased pressure in the space (as for example shown in Figure 2). The increased pressure in the spaces 15, 26, acts on the outer end of the piston, tending to move it inwards, so that for any given speed of rotation a given pressure will be maintained in the space. A pump (not shown) delivers oil to the space 15 under pressure, through a valve or cock and another valve (as shown in the specification of British Patent No. 628,499 or U. S. Patent 2,620,814). Maximum pressure in the space will be provided by the pump with the addition of that due to centrifugal action on the rotating fluid. This pressure will act on the outer end of the piston for at certain speeds the force on the piston due to centrifugal action will exceed the pressure acting on the outer end of the piston, and the piston will move fully outwards (shown Figure l) thereby completely closing the first inlet duct. v

Over a certain selected range of idling speeds, some pressure will be maintained in the space 15, since the spring will not be strong enough by itself to resist the centrifugal force on the piston. In a clutch of this kind, disengaging springs are usually provided but the mass of the piston will be so selected that the pressure in the space will be slightly in excess of that required to counteract the disengaging springs, so that, when idling, the friction surfaces of the clutch will be held in light contact.

In some circumstances, when idling, the pressure in the space 15, and therefore the space 26, is likely to exceed that required to balance the centrifugal action on the piston; for example when such a clutch is first started up with cold oil, considerable back pressure may result, and the pressure exceed the centrifugal action, the piston will move inwards thereby commencing to close the first inlet duct, which would cause increased pressure to act in the spaces 15, 26, with the result that the piston would move fully inwards thereby fully closing the first inlet duct 24 and engaging the clutch. This would cause the engine to stall. An irregular idling speed may produce the same result. With the present invention in such circumstances, the second groove 29 will open to the exhaust 30 as soon as movement commences to close the first inlet port 24, thereby exhausting, or greatly reducing, pressure in the space 26 at the outer end of the piston. It will be understood that the second inlet port 20 is` of small cross-sectional area as compared to the second outlet duct 30. The reduction in pressure in the space 26 thereby prevents further movement of the piston and causes it to take up a stable position whereby the pressure acting in the space 15 is in accordance with the centrifugal force due to the mass of the valve whether the oil is hot or cold, and irrespective of tendency to build up back pressure. t-f;

' it is fitted may over-run.

' down hill.

Upon over-running the spinner plate will apply drag to the friction member 12 and rotate the housing and engage the clutch.

In some applications, it is not convenient to provide the piston with suitable mass to maintain the required amount of pressure in the space 15 during the idling condition. It may be, for example that if the mass is sufficiently great for this purpose the speed at which full engagement takes place may be too low. ln these circumstances, the invention provides a second and inner piston 31. The piston 31 is of as low mass as convenient so as not to be greatly effected by centrifugal force. The inner end of the piston is provided with a bore 32 to enclose a spring 33 so arranged as to urge the piston outwards. In the outer position the piston will move beyond the first outlet duct 25 thereby preventing the escape of oil from the pressure space. The pressure of the fluid will however act on the outer end of the piston, i. e. in the space 34, tending to move it inwards against the spring 33, and to the position in which the first outlet duct 25 is partially or wholly opened. The exhaust 35 is provided to prevent liquid being trapped at the inner end of the piston 31.

at some minimum pressure, not less that required to balance the force from the spring 33.

Since the piston has some mass there will be variation in pressure with idling speed, but a pre-determined minimum pressure will always be maintained irrespective of the speed at which the clutch is idling. This ensures' that some minimum drag is maintained by the clutch. Should a clutch become completely free at some given idling speed, the driven part of the mechanism to which With the present invention shouldl over-run tend to take place, the drag will tend to increase the speed of the driving part and hence thev drag will be increased by the action of the piston 17. This results in automatic engagement. A further disadvantage resulting from a clutch which becomes completely free is the lag which takes place when speed is increased, since the friction surfaces must be moved into engagement before the increased pressure can take effect. The main purpose of the spring 19 is to move the piston 17 to the innermost position should the rotary valve body 17 become stationary, or nearly so.V This enables the clutch to be engaged, for as the first inlet duct is closed an engine may for example be started by towing, or running a vehicle to which the clutch is fitted With the spring 33 fitted, the spring 19 must exert sufiicient force to overcome the force from the spring 33, and to slide the piston 17 in its bore.

I claim:

l. In a hydraulically actuated friction clutch having friction elements engaged by fluid pressure, a centrifugal valve comprising, a rotary housing, a valve bore in said housing, a first inlet duct and a first outlet duct in said housing for supplying fluid under pressure to and exhausting said fluid from said valve bore respectively and a movable valve element in said bore, said valve bore being disposed with one end further from the axis of the said housing than' the oher end, so Vas to permit movement of said valve element under centrifugal action, the outer'end of said valve bore being permanently closed against escape of fluid therefrom, said valve element having openings whereby said inlet and outlet ducts are brought into communication when said valve element is in an intermediate position in said valve bore, for exhausting fluid under pressure, resilient means acting on said valve element in opposition to movement of said valve element caused by centrifugal force and serving to keep said valve element in exhaust closing positions during conditions of said housing from and including stationary, to a low predetermined speed of rotation thereof,

- a second inlet duct in said housing leading to the outer end of the said valve bore, serving to open fluid pressure to the outer end of said valve element whereby the pressure acts on the element in opposition to movement of said valve element caused by centrifugal force, and a second outlet duct controlled by said valve element to open to the outer end of the said valve bore just Vprior to commencing the inward movement of the valve element closing said first inlet duct.

2. A centrifugal valve as claimed in claim Vl having a second movable valve element 'in the inner end of said bore, second resilient means 4acting on said vsecond'valve During idling conditions therefore, pressure in the space 15 will be maintained s s element to cause movement of said second Valve in the Number Name Date same direction as caused by centrifugal force, and tend- 2,544,551 Black Mar. 6, 1951 ing to hold said second valve element in exhaust closing 2,619,978 Grandgirard Dec. 2, 1952 positions, closing said first outlet. FOREIGN PATENTS References Cited in the le of this patent Nugliaeg?4 F Country A Dgte 48 rance pr. 19

b UNHED STATES PATENTS 637,251 Great Britain May 17, 195o Num er Name Date 2,521,239 McDowall et al. Sept. 5, 1950 

